RAKwireless Support Request: RAK5860 (BG77) Constant Reboot Loop

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RAKwireless Support Request: RAK5860 (BG77) Constant Reboot Loop

Summary

Three RAK5860 modules (Quectel BG77) exhibit continuous reboot behavior (RDY flood) on three different baseboards. The modem reboots even in airplane mode (AT+CFUN=0), making LTE-M/NB-IoT connectivity impossible. The issue persists regardless of power source, antenna configuration, or baseboard used.

Hardware Configuration

Component Details
Core Module RAK4631 (nRF52840)
LTE Module 1 RAK5860 (BG77) — completely dead, no AT response
LTE Module 2 RAK5860 (BG77) — IMEI: 866349044282667, FW: BG77LAR02A04_01.002.00.000
LTE Module 3 RAK5860 (BG77) — IMEI: 866349044298937, FW: BG77LAR02A04_01.002.00.000
Baseboard 1 RAK19011 (Dual IO Base Board)
Baseboard 2 RAK19001 (Dual IO Base Board)
Baseboard 3 RAK19007 (Base Board)
Power Module RAK19012
Battery Panasonic NCR18650B (3400mAh, 4.1V)
LTE Antenna Original RAK5860 LTE antenna (U.FL)
SIM 1 Digital Republic IoT, ICCID: 89410229754900203433
SIM 2 Digital Republic IoT, ICCID: 89410229754900203441

Problem Description

All RAK5860 modules reboot continuously during operation. The BG77 modem responds to initial AT commands after power-on, but starts sending repeated “RDY” messages (indicating reboot) within seconds. This happens:

  • With RF active (network search): ~7 reboots in 15 seconds
  • In airplane mode (AT+CFUN=0, RF off): 2 reboots in 10 seconds
  • Without antenna connected: reboots continue
  • With antenna connected: reboots continue
  • The modem never achieves network registration (CEREG always 0,2 = searching)
  • CSQ is always 99,99 (no signal)
  • GPS commands all return ERROR

Power-On Sequence Used

// Enable RAK5860
pinMode(WB_IO1, OUTPUT);
digitalWrite(WB_IO1, HIGH);

// Configure BG77 pins
pinMode(WB_IO2, OUTPUT);   // POWER_KEY
pinMode(WB_IO5, OUTPUT);   // RESET_PIN
digitalWrite(WB_IO5, LOW); // RESET inactive

// UART
Serial1.begin(115200);
delay(1000);

// Power Toggle
digitalWrite(WB_IO2, LOW);
delay(300);
digitalWrite(WB_IO2, HIGH);
delay(2000);
digitalWrite(WB_IO2, LOW);
delay(10000);  // Wait for modem startup

Test Results

Test 1: Module 2 on RAK19011

ATI      → Quectel BG77, Revision: BG77LAR02A04
AT+GSN   → 866349044282667
AT+CPIN? → +CPIN: READY
AT+QCCID → 89410229754900203433
AT+CSQ   → +CSQ: 99,99
AT+QCSQ  → +QCSQ: "NOSERVICE"
AT+QENG  → +QENG: "servingcell","SEARCH"
AT+CEREG → +CEREG: 0,2
AT+COPS=? → Modem crashes (RDY reboot loop)

Tested IoT modes: Cat-M1 (iotopmode=0), NB-IoT (iotopmode=1), both (iotopmode=2)
Tested slots: A and B — identical result

Test 2: Module 3 on RAK19001

ATI      → Quectel BG77, Revision: BG77LAR02A04
AT+GSN   → 866349044282667
AT+CPIN? → +CPIN: READY (SIM 2)
AT+QCCID → 89410229754900203441
AT+CSQ   → +CSQ: 99,99
AT+QCSQ  → +QCSQ: "NOSERVICE"
AT+CEREG → +CEREG: 0,2
AT+COPS=? → Modem crashes (RDY reboot loop)

Tested: Swapped Main and GNSS antenna — no difference

Test 3: Module 3 on RAK19007 (Reboot Detection Test)

AT+CFUN=0 → OK (airplane mode)
  → 2 reboots detected in 10 seconds WITH RF OFF

AT+CFUN=1 → RDY RDY RDY
  → 7 reboots in 15 seconds with RF on

Total reboots during full test: 18

Band config (factory default): 0x100002000000000f0e189f
iotopmode: 2 (Cat-M1 + NB-IoT)
nwscanseq: 0203
servicedomain: 2

Test 4: Power Supply Variations on RAK19007

Power Source Result
PC USB only RDY reboot loop
Pi5 PSU (5V/5A) via USB RDY reboot loop
Battery (NCR18650B, 4.1V) via RAK19012 only RAK5860 LEDs don’t light up at all
Battery + Pi5 USB simultaneously RDY reboot loop
No antenna + Pi5 USB RDY reboot loop

SIM Verification

Both SIM cards were tested in an Android smartphone:

  • Immediately connected to Sunrise network (4G/LTE)
  • Internet working perfectly
  • Good signal strength

SIM provider (Digital Republic) confirms connectivity includes: 3G, 4G-LTE, 5G, LTE-M, NB-IoT
APN: “internet” (confirmed by provider)

Key Observations

  1. Modem reboots in airplane mode (CFUN=0) — this rules out RF power draw as the sole cause
  2. Reboots are more frequent with RF on — RF activity worsens the issue but is not the only trigger
  3. Module 1 is completely dead — no response to any AT command, no LEDs
  4. Modules 2 and 3 exhibit identical behavior — same firmware, same reboot pattern
  5. AT commands work initially — modem boots, responds to AT, ATI, CPIN, QCCID correctly
  6. GPS is also non-functional — AT+QGPS=1 returns ERROR on all modules
  7. Battery alone cannot power RAK5860 — LEDs don’t light up, only works with USB
  8. Same setup worked ~2 weeks ago — a previous RAK5860 module (now defective = Module 1) successfully sent HTTP data via LTE-M

Questions for RAKwireless

  1. Is there a known issue with BG77 firmware version BG77LAR02A04_01.002.00.000 causing reboot loops?
  2. Is there a recommended firmware update for the BG77 on RAK5860?
  3. Could this be a batch/production defect? (All modules purchased around the same time)
  4. Is there a minimum VBAT voltage or current requirement for the RAK5860 that might not be met by the RAK19012 + NCR18650B combination?
  5. Why does the RAK5860 not power on from battery alone (via RAK19012) even though the baseboard (RAK4631) runs fine?
  6. Is the power-on sequence shown above correct for the RAK5860?
  7. Are there any known compatibility issues between RAK4631 BSP v1.3.3 and RAK5860?

Environment

  • Arduino BSP: rakwireless:nrf52 v1.3.3
  • Board: WisCoreRAK4631Board
  • TinyUSB Library: v3.7.5
  • Location: Thurgau, Switzerland (Sunrise network area)
  • Date of testing: April 14, 2026

Contact

Dirk Schumacher

Switzerland

2

Welcome to the forum @SCDI

Not sure where you got the information for your code.

  1. WB_IO5 is not used with the RAK5860, it makes no sense to set it
  2. In the power toggle sequence, you leave with digitalWrite(WB_IO2, LOW);, which means power is off. This is actually the power supply for the GNSS antenna and does not influence the power supply of the RAK5860. That would be WB_IO1, which is set correct to HIGH.

Did you try some of our simple examples in from our WisBlock Examples for RAK5860?

3

It looks like this is a power problem with the BG77 or RAK5860, not the firmware.

Reboots in CFUN=0 and gets worse with RF, which is a classic brownout. AT+COPS=? starts a high current → voltage dips → RDY loop.

Check VBAT, try a stable 4V supply (2A+), and add bulk caps. It’s likely that the BG77 isn’t getting clean power.

1 Like